The invention relates to a coupling adapted to connect radially rotating shafts comprising: a first main coupling member for connection to a first shaft, a second main coupling member for connection to a second shaft, and floating intermediate member means, the latter being connected to said first and second main coupling members by link members.
Prior art couplings for angle-true transmission of rotary movements between parallel shafts having variable radial offset of the shafts comprise an intermediate member which is connected to each of the two coupling members by linkages of at least three mutually parallel link members. (See Kurt Rauh "Praktische Getriebelehre", 53 and 54, Springer-Verlag, Berlin, 2d edition, volume 1, page 31). The intermediate member is always kept parallel to the first (driving) coupling member by the link members, so that it rotates angle-true with this first coupling member. In the same way, the intermediate member is in driving connection with the second (driven) coupling member through parallel link members, so that the second coupling member, in turn, follows the intermediate member and thus the first coupling member in angle-true manner. The length of the link members is smaller than the spacing of the pivot points on the coupling members and the intermediate member, respectively, so that the link members may rotate past each other with continuous rotary movement. In a prior art embodiment of such a coupling (German Pat. No. 1,233,667) the intermediate member comprises a floating disc-shaped body.
This prior art coupling is based on the characteristic of a parallel link member linkage to guide one part parallel with respect to another one. By using two such parallel link member linkages in series, the linkages being arranged to be movable relative to each other in scissor-like manner, two shafts can be coupled with each other, with the shafts being radially offset or also movable relative to each other within an area determined by the length of the link members. In a coupling operating in accordance with this principle each of the link members is, during each revolution, subjected once to compression and once to tension while rotating through 360.degree. relative to the intermediate member. Therefore the pivot pin moves back and forth in its pivot bore due to the inevitable clearance. This results in vibrations, noise and increased wear, particularly when large torques are transmitted. In addition, in the prior art coupling each link member is engaged in the torque transmission in accordance with a sine function of the angle of rotation, thus only to a small proportion in certain ranges of angle. On the other hand the number of the link members that can be used to transmit the torque is limited to three for geometrical reasons. This also causes problems with regard to the transmission of torques.
It is an object of the invention to provide a coupling of the type initially defined herein which is adapted to transmit high torques.
A more specific object of the invention is to provide such a coupling in which during rotation of the shaft in a particular direction each one of the link members is loaded in one direction only, thus either by tensile load or by compression load; in which more than three link members may be provided if required; in which each one of the link members is used substantially completely to transmit torque during each phase of the revolution; and in which during each revolution each one of the link members carries out only a limited rocking movement if the axes are radially offset.
According to the invention, these objects are achieved in that the intermediate member means comprise at least two intermediate coupling members rotatable with respect to each other about an axis, each one of the intermediate coupling members being connected to the first (e.g. input) of the main coupling members through one link member and to the second (e.g. output) of the main coupling members through another link member. In a coupling of the invention the first, for example driving, main coupling member is connected with the second main coupling member through a link member, an intermediate coupling member and a further link member. Another drive connection is established from the first main coupling member, another link member, a second intermediate coupling member and still another link member again to the second main coupling member. The intermediate coupling members are rotatable relative to each other and floating. If the axes of the first and second shafts are in alignment, the whole assembly operates like a rigid connection between the shafts and rotates about the common shaft axis. In this case the link members do not move relative to the main coupling members and intermediate coupling members and, in each phase of the revolution take part equally in the torque transmission. If the axes of the shafts are parallel but slightly offset, this offset of the axes will be compensated for by relative rotation of the intermediate coupling members, providing the required additional degree of driven Also in this case the driver main coupling member is moved along by the driving one through the link members and the intermediate coupling members, only the link members making a rocking compensating movement.